1. Field of the Invention
The present invention relates to a method of performing relay communication by constructing a relaying terminal group and a transmitting/receiving terminal group and then using cooperation between the groups, so as to realize effective communication between a base station and one or more terminals in a next generation cellular communication system which uses a band of several tens of GHz.
2. Description of Related Art
Currently, a cellular communication system provides voice or data service to users in a relatively wide area using a 2 GHz or lower frequency band. In the case of current service, since a low speed service, the maximum speed of which is several Mbps, is provided, the narrow bandwidth does not matter. Further, since the 2 GHz or lower frequency band has relatively good propagation characteristics, communication can be sufficiently realized, even though a Line-Of-Sight (LOS) channel is not ensured. Further, in order to provide service to regions, such as an underground and mountain regions, which the signals of a base station cannot reach, service areas have been expanded using repeaters. Furthermore, research has been widely conducted so as to improve the strength of a link or increase transmission speed through the cooperation between a plurality of terminals.
Systems that use a high frequency band of 60˜70 GHz for communication include a very short-range communication system, such as a Wireless Personal Area Network (WPAN), and a wireless trunk system for substituting for a wired trunk between buildings. The WPAN defines a system for providing several Gbps high-speed data communication using a high frequency band with a maximum bandwidth of 1 GHz. In the case in which a high frequency carrier is used, there is an advantage in that a wide bandwidth can be acquired but the propagation characteristics are not desirable. Therefore, in the case in which an omnidirectional antenna is used, communication is not possible if a terminal locates out of a region of several tens of meter in which a LOS channel is ensured. Therefore, the system has a restriction in that it can only be used for short-range communication.
Meanwhile, a wireless trunk system for connecting buildings has solved a problem of wave propagation distance using an antenna having high directivity, such as a parabolic antenna. As a method for utilizing antenna gain, a parabolic antenna having strong directivity can be used, as in a wireless trunk system, but the antenna can be used only for point-to-point communication. Therefore, in order to perform point- to-multipoint communication while maximizing antenna gain, directivity of the antenna must be varied at any time using an array antenna.
Until now, in consideration of propagation characteristics, most communication systems using a high frequency of several tens of GHz have been used in a WPAN, which has a very narrow service area, and have used an antenna with which a LOS channel is reliably ensured and which has a high gain like a parabolic antenna. However, in the case in which this is expanded to a general communication system, such as a cellular communication system, a high gain can be realized using an antenna array, but it is considerably difficult to support a user for whom a LOS channel is not ensured.
That is, although the use of a repeater can be considered as an example of supporting a user for whom a LOS channel is not ensured, this may impose a burden on the entire communication system. When an existing low frequency is used, the shadow region is not wide, so that a repeater can be installed. However, in the case in which a frequency of several tens GHz is used, the portion of the shadow region increases, so that there is a burden in that a large number of repeaters must be installed, and a large number of non-LOS channels may be generated between the links of repeaters and terminals, so that there is a problem in that the communication between a base station and a terminal is not supported at all in a non-LOS channel between the repeater and a terminal.
Currently, a cellular communication system uses a low frequency band which has excellent propagation characteristics, and the International Telecommunication Union (ITU) is considering a band of several tens of GHz as a candidate frequency band for a next generation cellular communication system. The high frequency band which will be used in the next generation cellular communication system has poor propagation characteristics. Therefore, when a LOS channel is not ensured, the intensity of received signals is insufficiently small, and thus communication cannot be realized.